Base of a chair



FIG. 1 is a top front side perspective view of the new design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a top plan view thereof;

FIG. 4 is a right side elevation view thereof;

FIG. 5 is a bottom plan view thereof; and,

FIG. 6 is a rear elevation view thereof;

The broken lines illustrate the environmental structure of the base of the chair, and form no part of the claimed design. 

The ornamental design for a base of a chair, as shown and described. 